The present invention relates to the use of coaxial pulse tube refrigerators in MRI or NMR systems, particularly in the neck tube of such systems.
Coaxial pulse tube refrigerators are described in a paper entitled xe2x80x9cDevelopment of a Practical Pulse Tube Refrigerator: Coaxial design and the influence of viscosityxe2x80x99 by R. N. Richardson in Cryogenics 1988 Vol. 28 August, pages 516-520. A pulse tube refrigerator (PTR) comprises two tubes, a pulse tube and a regenerator tube, in which an oscillating pressure-wave of gas produces the cooling effect. The paper states that the concentric pulse tube design provides a convenient, compact configuration for achieving high heat pumping rates. Instead of placing the regenerator concentrically around the pulse tube which is the preferred configuration, the pulse tube occupies the annular space and surrounds the regenerator at the center.
One object of the present invention is to incorporate a coaxial pulse tube refrigerator into the neck portion of an MRI and NMR system.
According to the present invention there is provided an MRI or NMR system comprising a magnet assembly immersed in a cooling liquid contained within a vessel, and having an orifice in the form of a neck-tube. The neck-tube is adapted to house a pulse tube refrigerator which is in the form of an annulus or a section of an annulus.
The pulse tube refrigerator may have an enhanced surface structure which is either a natural or an artificial structure.
The pulse tube refrigerator has its regenerator tube in the form of an annulus which is concentric and coaxial and in contact with either the inside or outside of its pulse tube.
The regenerator tube or pulse tube may also act as a suspension element.